316 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



Fig 20 The effect of the freeze on unheated Lisbon lemon tree. Compare 



fig. 21. 



In view of the great amount of detailed record-keeping involved 

 for each individual tree, it was found necessary to limit the number 

 of trees for observation. In order to combine reliability of data and 

 limit the number of trees to the smallest possible number, the fol- 

 lowing plan of plot arrangement was carried out. First, comparable 

 orchards were selected. Then a plot of ten trees in each orchard was 

 arranged on the following basis: Two adjoining trees were marked 

 for observation. Counting these trees as numbers 1 and ^2, respec- 

 tively, the ninth and tenth trees in the same row were also marked. 

 Corresponding trees, ten rows from this row, were then marked, so 

 that the marked trees were the two end trees in a square of one 

 hundred trees. In addition to these eight trees, two trees in the 

 middle of the square were also marked, thus completing the plot. 



